A breech of this type is known from DE 103 32 962 B3. The breech disclosed in this publication features a bolt assembly that is guided within a housing such that it is rotatable about its longitudinal axis and axially displaceable in the longitudinal direction of the firearm, a striking pin that is axially movable in the bolt assembly and a breech block that is arranged on the rear end of the bolt assembly and in which a cocking mechanism is accommodated that can be actuated with an actuating element and serves for tensioning and relaxing a striking pin spring acting upon the striking pin. In this known breech, the actuating element consists of a cocking lever that is rotatable within the breech block about a bearing pin arranged perpendicular to the longitudinal axis of the firearm and can be turned by means of a rearwardly protruding handle part. An articulated lever in the form of a crank-and-rocker linkage is coupled to a disk-shaped part of the cocking lever. This articulated lever is engaged with a tensioning rod, by means of which the striking pin spring can be respectively tensioned and relaxed.